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Physiology Week 6 Notes

by: Alesa Taylor

Physiology Week 6 Notes 3014

Marketplace > Mississippi State University > 3014 > Physiology Week 6 Notes
Alesa Taylor
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the end of chapter 6
Human Physiology
James Stewart
Class Notes
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This 5 page Class Notes was uploaded by Alesa Taylor on Friday February 19, 2016. The Class Notes belongs to 3014 at Mississippi State University taught by James Stewart in Spring 2016. Since its upload, it has received 59 views.


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Date Created: 02/19/16
2/16/16  Voltage is a difference in electric potential between two points o Separation of positive and negative electric charges on opposite sides of a resistive barrier o Resting membrane potential of a cell arises from the separation of intracellular potassium ions from anions across the cell membrane of the cell  Concentration gradient of potassium ions must be set up using the Na+/K+- ATPase (sodium-potassium pump) creating a resting (unstimulated) cell and membrane that has the potential to conduct electrical signal or action potential o 3 sodium ions go out of the cell o 2 potassium ions go into the cell o It creates a deficit of positive ions inside the cells, so inside the cell is more negative than the outside- doesn’t happen because of equilibrium potential, requires energy to maintain  Resting membrane potential- -70mV, the inside of the cell is much more negative than the outside, defined as a relatively stable, ground value of transmembrane voltage in animal and plant cells  Threshold potential- must be reached for action potential to “fire”, remember these are graded potentials, requires -55 mV to reach excitatory potential  Inhibitory potential- too low is subthreshold potential, too high is suprathreshold potential  Depolarization- membrane potential becomes less negative; either positively charged ions enter the cell or negatively charged ions leave the cell o the sodium/potassium pump has leaky channels, especially leaky to potassium  repolarization- returns to the normal resting potential, either negatively charged ions enter the cell or positively charged ions leave the cell; re- established by the Na+/K+ ATPase pump  hyperpolarization- becomes more negative; either the negatively charged ions entering the cell or positively charged ions leaving; re-establishing membrane potential  spatial summation- interaction of graded potentials from different receptors will “meet” at the axon hillock, adds together to reach action potential; energy comes from different sites  temporal summation- interaction of graded potential that occurs at slightly different times at the axon hillock; adds together to reach action potential; sums up at different times  axon hillock- Acts as a decision point for the neuron, creates an action potential only if the combination of graded potentials causes the axon hillock to depolarize beyond threshold; summation of graded potentials allows integrated inputs from many different stimuli  “all-or-none”- does or does not occur, once an action potential has been initiated by the opening of Na+ channels it always proceeds to the conclusion; never stops halfway or fails to reach peak depolarization  self-propagation- individual action potential does not actually travel across the axon; action potential in one part of the axon triggers other action potential in adjacent area of the axon membrane; every action potential is identical without degradation of the signal; like dominoes  electric currents- go between ion channels of axon Na+ ions entering; voltage-gated channels; depolarize the membrane immediately surrounding the channel; spreads through the dendrites and cell body; wave of depolarization along the axon which triggers action potential further downstream  VOLTAGE GATED CHANNELS- memorize!!!! 1. Action potential is due to the opening and closing of voltage-gated ion channels 2. As the membrane potential reaches threshold at the axon hillock, sodium channels begin to open- beginning of depolarization 3. Sodium influx further depolarizes the region causing more sodium channels to open; increase permeability which increases sodium in cell 4. Equilibrium potential is +60mV reached 5. Sodium channels close- ends depolarization 6. Sodium channels close- ends depolarization 7. Threshold depolarization of the membrane at the axon hillock causes a change in membrane potential, which causes potassium channels to open; same time that the sodium channels close 8. Potassium are slow channels 9. Potassium channels will slowly close as equilibrium potential of potassium is reached -90mV 10. As potassium ions try to get to their equilibrium- hyperpolarization “overshoot”  Supporting cells in the central nervous system o Astrocytes – most abundant; controls ionic environment around neurons o Microglia – smallest and least abundant; macrophages of CNS engulfing microbes, injured or dead neurons o Ependymal cells – form epithelium lining central cavity of spinal cord and brain; circulate cerebrospinal fluid with cilia o Oligodendrocytes – produce myelin sheaths that insulate neurons  Supporting cells in peripheral nervous systems o Satellite cells – surround neuron cell bodies to support and protect o Schwann cells (neurolemmocytes) – surround axons in PNS and form myelin sheaths  Myelin – lipoprotein that surrounds thicker axons  Structure: Layers consist of concentric layers of plasma membrane of supporting cell  Function: insulating layer that prevents leakage of electrical current from axon to increase speed of the impulse conduction along the axon; energy efficient  Nodes of Ranvier – gaps in myelin sheath; nerve impulses do not travel along myelin-covered regions but jump from node to nodes- salutatory conduction  Synaptic Signal Strength presynaptic factors o Neurotransmitter availability  Availability of precursor molecule  Activity of rate limiting enzyme o Axon terminal membrane potential o Axon terminal calcium concentration  Drugs and diseases  Neurotransmitter release- Is determined by axon terminal membrane potential and axon terminal calcium concentration; it can be affected by drugs and diseases; it requires the removal of the unbound transmitter in order to reuptake, diffuse away from cleft, and do enzymatic transformation into inactive substances  Postsynaptic factors- has to do with electrical potential status, it is excitable (excitatory postsynaptic potential or EPSP)- depolarizing event on postsynaptic cell membrane, can be inhibitory (inhibitory postsynaptic potential or IPSP)- hyperpolarizing event on postsynaptic cell membrane, can change the effects of other neurotransmitters  Neurotransmitter characteristics- synthesized in neurons they are released by the presynaptic cell following depolarizationinds to a postsynaptic receptor and causes and effect  Acetylcholine (ACh)- Major neurotransmitter in PNS at neuromuscular junction and brain, made up of cholinergic neurons o ACh receptors:  Nicotinic receptors- Na+ driving force  Muscarinic receptors- G proteins  Catecholamines- formed from the amino acid tyrosine: dopamine, norepinephrine, epinephrine  Receptors are metabotropic and use second messengers  Major classes of receptors: o Alpha-adrenergic receptors-PLC;Ca2+ o Beta-adrenergic receptors-cAMP; K+ channels  Amino acids o Glutamate, aspartate, glycine, GABA  Biogenic amines o Serotonin  Neuropeptides o Opioids and analgesics o Endogenous opioids: Endorphins  Gases o Nitric oxide  Purines o ATP and adenosine  Functional organization of peripheral nervous system o Sensory inputs and classifications- General = Widespread; Special = Local  Somatic sensory: o General – skin and body walls, touch, pain, pressure, vibration, temperature and proprioception o Special – hearing, equilibrium, vision, smell  Visceral sensory: o General – stretch, pain, temperature, chemical changes, nausea and hunger o Special – Taste  Motor outputs and classifications- General = Widespread  Somatic motor or voluntary motor: o General – motor innervation of all skeletal muscles  Visceral motor or involuntary motor: o General – motor innervation of smooth and cardiac muscle and glands o Autonomic nervous system  Parasympathetic division  Sympathetic division  Somatic Motor Pathways- controls skeletal muscle performance, usually under conscious (voluntary) control; also known as voluntary nervous system o Some efferent pathways are not under conscious control- reflex control o Rapid involuntary movement in response to a stimulus (like the patellar reflex, gag reflex, and blink reflex like in lab)  Somatic Pathway Characteristics 1. Control only one type of effector organ (skeletal muscle) 2. Cell bodies are located in the CNS 3. Long and monosynaptic (one synapse between CNS and effector organ 4. Axons split into a cluster of axon terminals at the neuromuscular junction 5. Synaptic cleft between the motor neuron and the muscle is very narrow to communicate more rapidly with their effectors 6. Release the neurotransmitter acetylcholine 7. Effect on the muscle is always excitatory; muscles relax only when the associated motor neurons are at rest  Autonomic Nervous System (ANS) Pathways- Contain 2 neurons in series:  Preganglionic neuron o Located within the CNS; will synapse with several postganglionic neurons  Postganglionic neuron (Autonomic ganglia) o Located in with the PNS and will synapse with the effector organ o At the effector organ, neurotransmitters release to diffuse through extracellular fluid to receptors on effector organ  2 Divisions:  Parasympathetic – controls routine maintenance or “housekeeping” functions when the body is at rest o Digestion and waste mobility  Sympathetic – controls “fight or flight” response o Increases heart rate, vasoconstriction, respiration, pupil dilation and cell metabolism o Decreases non-essential functions like digestion and waste mobility  Difference between divisions of ANS: There are 3 main anatomical differences: 1. Cell bodies of preganglionic sympathetic and parasympathetic neurons are located in different regions of the CNS. a. Sympathetic: originate in the thoracic and lumbar regions of the spinal cord (Thoracolumbar division) b. Parasympathetic: originate either in the hind brain or in the sacral region of the spinal cord (cranial sacral division) 2. Locations of the ganglia differ a. Sympathetic: found in a chain that runs close to the spinal cord having a short preganglionic neurons and long postganglionic neurons b. Parasympathetic: located close toe the effector organ having long preganglionic and short postganglionic neurons 3. Differing relationship between the preganglionic and postganglionic neurons a. Sympathetic: preganglionic neurons form synapses with 10 or more postganglionic neurons; effects will be widespread b. Parasympathetic: preganglionic neurons form synapses with 3 or fewer postganglionic neurons; effects will be localized  3 important features of the ANS underlie its ability to maintain homeostasis: o Duel innervation: most organs receive input from both sympathetic or parasympathetic nervous systems to regulate effector organs; checks and balances  Antagonistic action: one is stimulatory and other is inhibitory o Parasympathetic causes bronchioles to constrict by causing smooth muscles to contract o Sympathetic causes dilation through relaxation of smooth muscle  Basal tone (Basal tone activity): under resting conditions autonomic neurons will continually signal  Reflex Arcs of ANS- Neural circuits that do not involve the conscious centers of the brain.  Example, blood pressure regulation- receptors detect when blood pressure falls, sends signals to medulla, increase sympathetic activity, decrease parasympathetic activity, adjust heart rate, stroke volume, and vasoconstriction, returning blood pressure back to normal o Negative feedback loop


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